﻿// HyperbolicInterpolator.cs
//
// Author:
//       Xavier Fischer 
//
// Copyright (c) 2019 
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace DEM.Net.Core.Interpolation
{
    /// <summary>
    /// HyperbolicInterpolator : gives smoother results, but can skip small flat areas
    /// Other implementation described briefly in article.
    /// 
    /// Source : http://www.geocomputation.org/1999/082/gc_082.htm
    /// </summary>
    public class HyperbolicInterpolator : IInterpolator
    {
        public double Interpolate(double southWestHeight, double southEastHeight, double northWestHeight, double northEastHeight, double x, double y)
        {
            double h1 = southWestHeight, h2 = southEastHeight, h3 = northWestHeight, h4 = northEastHeight;
            // hyperbolic
            double a00 = h1;
            double a10 = h2 - h1;
            double a01 = h3 - h1;
            double a11 = h1 - h2 - h3 + h4;
            double hi_hyperbolic = a00 + a10 * x + a01 * y + a11 * x * y;

            return hi_hyperbolic;
        }
    }
}
